Generic service switching devices, for example motor circuit breakers, have at least one pole current path with a double contact point and two fixed contact pieces and two moveable contact pieces arranged on a moveable contact link.
In this case, the contact link is acted on by means of a thruster in the opening direction and by means of a contact pressure spring in the closing direction.
Furthermore, generic service switching devices comprise an electromagnetic release, whose armature, in the event of the occurrence of a short-circuit current in the pole current path, both acts on the contact link in the opening direction via the thruster and unlatches the latching point of a switching mechanism, with the result that the switching mechanism acts on the contact link permanently counter to the force of the contact pressure spring so as to open said contact link via an active lever.
Directly after the contact link has been acted upon and therefore directly after the interruption of the short-circuit current in the pole current path, the electrodynamic reaction of the electromagnetic release breaks down and the contact link is acted upon again in the direction towards its closing position by the force of the contact pressure spring.
Owing to the relatively high level of mechanical inertia of the switching mechanism, compared with that of the system comprising the armature and the thruster, the active lever lags the thruster movement in order to keep the contacts permanently open by means of the switching mechanism.
Under unfavourable conditions it may arise that the contacts have already been closed again by the contact pressure spring before the switching mechanism can bring about a permanent opening via the active lever and the thruster. This is then referred to as an occurrence of contact bounce, which is undesirable.
In order to avoid contact bounce, DE 10 2006 055 007.2 proposes using a slide and a striker pin as thruster, of which the striker pin is guided within the slide, the arrangement comprising the slide, the striker pin, the contact link, the active lever and the armature being designed such that, in the event of a short circuit, the armature accelerates the striker pin very rapidly owing to the small mass thereof and therefore acts very quickly on the contact link. In this case, the slide lags the striker pin before the active lever, via the slide, keeps the contact link permanently in the open position counter to the contact pressure force.
If the contact link has been acted upon and, as a result, the short-circuit current has been interrupted, the force effect of the armature on the striker pin also ends. The contact link is now pushed in the closing direction again by the force of the contact pressure spring.
The slide, which lags the striker pin, can brake this countermovement of the contact link, with the result that the contact link is prevented from closing the contacts before the active lever, which still continues to lag the striker pin owing to the relatively high level of mechanical inertia of the switching mechanism, finally keeps the contact link permanently in the open position via the slide.
In this case, the inertia of the striker pin and a low level of friction between the mechanical striker pin and the slide are utilized such that the striker pin keeps the contact link open for a sufficient period of time until the effect of the slide sets in during the triggering of the switching mechanism.